HUMAN PARVOVIRUS B19 NONSTRUCTURAL (NS1) PROTEIN INDUCES APOPTOSIS INERYTHROID LINEAGE CELLS

Infection of erythroid-lineage cells by human parvovirus B19 is charac terized by a gradual cytocidal effect, Accumulating evidence non impli cates the nonstructural (NS1) protein of the virus in cytotoxicity, bu t the mechanism underlying the NS1-induced cell death is not known. Us ing a stringent regulatory system, we demonstrate that NS1 cytotoxicit y is closely related to apoptosis. as evidenced by cell morphology, ge nomic DNA fragmentation, and cell cycle analysis with the human erythr oleukemia cell line K562 and the erythropoietin-dependent megakaryocyt ic cell line UT-7/Epo. Apoptosis was significantly inhibited by an int erleukin-1 beta (IL-1 beta)-converting enzyme (ICE)/CED-3 family prote ase inhibitor, Ac-DEVD-CHO (CPP32; caspase 3), whereas a similar inhib itor of ICE (caspase 1), Ac-YVAD-CHO, had no effect, Furthermore, stab le expression of the human Bcl-2 proto-oncogene resulted in near-total protection from cell death in response to NS1 induction, Mutations en gineered into the nucleoside triphosphate-binding domain of NS1 signif icantly rescued cells from NS1-induced apoptosis without having any ef fect on NS1-induced activation of the IL-6 gene expression which is me diated by NF-kappa B. Furthermore, using pentoxifylline, an inhibitor of NF-kappa B activation, we demonstrate that the NF-kappa B-mediated IL-6 activation ba NS1 is uncoupled from the apoptotic pathway. This f unctional dissection indicates a complexity underlying tile biochemica l function of human parvovirus NS1 in transcriptional activation and i nduction of apoptosis. Our findings indicate that NS1 of parvovirus B1 9 induces cell death by apoptosis in at least erythroid-lineage cells by a pathway that involves caspase 3, whose activation may be a key ev ent during NS1-induced cell death.